Apparatus for digital imaging in the head region of a patient

ABSTRACT

An apparatus for Digital Imaging in the Head Region of a Patient includes an X-ray source and an X-ray sensor, supported on i a rotary arm supported on a structure by a motor driven translation and rotation means. The rotary arm is provided with adjustment means for varying the distance between the source and the sensor. The apparatus comprises a single sensor for both panoramic imaging and computed tomography, and has a control unit, that controls the source, the sensor, the adjustment means, and the translation and rotation means and operates the apparatus in a basic operation mode for bigger patients and in an alternative operation mode for smaller patients, in which the distance between the source and the sensor is reduced as compared to the distance used for the basic operation mode.

FIELD OF THE INVENTION

The invention relates to an apparatus for digital imaging in the headregion of a patient comprising:

-   -   a source for generating X-ray radiation;    -   a sensor for detecting X-ray radiation, which is generated by        the source and passes through a patient;    -   a rotary arm for arranging the source and the sensor thereon in        such a way as to be opposed to each other, wherein the rotary        arm is provided with adjustment means for varying the distance        between the source and the sensor;    -   a supporting structure for supporting the rotary arm, wherein        motor driven translation and rotation means are interposed        between the rotary arm and the supporting structure.

BACKGROUND OF THE INVENTION

US 2007/0030950 A1 discloses a combined panoramic and computedtomography (=CT) apparatus for dental imaging. The apparatus includes anX-ray source and an X-ray sensor unit provided either with a panoramicsensor part or a CT sensor part for detecting X-rays, which aregenerated from the X-ray source and pass through a patient. Theapparatus further includes a rotary arm for arranging the X-ray sourceand the X-ray sensor unit thereon in such a way as to be opposed to eachother. The rotary arm is held by a supporting member. Driving means areprovided that allow to vary the distance between the X-ray source andthe X-ray sensor unit arranged opposed to each other with respect to therotary arm.

The known apparatus can conduct panoramic imaging and CT imaging, andprovides the optimum enlargement ratio according to whether theapparatus is operated in the panoramic imaging or the CT imaging mode.The optimum enlargement ratio is achieved by varying the distancebetween X-ray source and the X-ray sensor unit.

The known apparatus is only optimal for adult patients having a normalsize. The imaging of smaller persons particularly children, however, mayrequire modifications.

Proceeding from this related art, the present invention seeks to providean apparatus for digital imaging in the head region also optimized forsmaller patients, in particular children.

This object is achieved by an apparatus having the features of theindependent claim. Advantageous embodiments and refinements arespecified in claims dependent thereon.

SUMMARY OF THE INVENTION

The apparatus comprises a single sensor for both panoramic imaging andcomputed tomography in the head region of the patient, and a controlunit, that controls the source, the sensor, the adjustment means and thetranslation and rotation means. The control unit is arranged foroperating the apparatus in a basic operation mode for bigger patientsand in an alternative operation mode for smaller patients, in which thedistance between the source and the sensor is reduced as compared to thedistance used for the basic operation mode. By reducing the relativedistance between the source and the sensor, the dose rate and/or theexposure time can be reduced thus diminishing the radiation risk of achild to be examined.

For the alternative operation mode, the control unit can move bothsource and sensor towards each other, thus allowing the enlargementratio to be preserved.

In an alternative embodiment, the apparatus is set up for thealternative operation mode by the control unit moving only the sensortowards the source that is fixed to the rotary arm. Thus, the rotary armneed only be provided with means for moving the sensor towards thesource.

In a modified embodiment, the distance for the alternative operationmode is reduced by shifting the rotation axis. The source is kept fixedwith respect to the rotary arm and the control unit reduces the distanceby shifting a rotation axis of the rotary arm in the direction of thesensor and by moving the sensor towards the source. This allows to keepthe enlargement ratio for both operation modes unchanged.

In the modified embodiment, a special operation mode may be used forcomputer tomography, since for computer tomography the rotation axis maybe moved on a trajectory around a virtual rotation axis that is locatedat the object to be imaged.

For enhancing the safety of the apparatus, the sensor is moved within ahousing that is stationary with respect to the rotary arm.

The adjustment means may comprise means for positioning the sensor thatare selected from the group comprising:

-   -   a mechanism including means for a lateral motion with respect to        a longitudinal axis of the rotary arm,    -   a mechanism including means for a swivelling motion with respect        to the rotary arm,    -   a scissor mechanism for varying the distance between a base        attached to the rotary arm and a support structure of the        sensor,    -   a linear mechanism for moving the sensor along a guiding        structure in the direction of the source, and    -   combinations thereof.

A mechanism enabling a lateral movement of the sensor allows to adjustthe sensor to the panoramic and CT imaging mode. It may also be used tocompensate for the lateral shift of the sensor if the swivellingmechanism is used for adjusting the distance between source and sensor.A mechanism for performing a swivelling motion has the additionaladvantage of rapid position change. The same holds for a scissormechanism. The linear mechanism offers less speed for changing theposition but is particularly stable and reliable.

The adjustment means are generally motor driven so that the operatordoes not have to take care for adjusting the distance between source andsensor.

The apparatus can be provided with a primary collimator that is locatedbetween the source and the patient and that is opened wider in thealternative operation mode than in the basic operation mode in order totake into account the greater beam width that is required for thealternative operation mode.

In one embodiment, the radiant intensity and thus the absorbed dose rateis reduced in the alternative operation mode by reducing the X-raygenerating current and/or voltage of the source.

The radiant intensity and thus the absorbed dose rate may particularlybe reduced by the square of the ratio of distance between source andsensor in the alternative operation mode to the distance between sourceand sensor in the basic operation mode so that the exposure time may bekept unchanged.

Alternatively or additionally the exposure time of the sensor is shorterin the alternative operation mode than in the basic operation mode.

The enlargement ratio is usually the same in the alternative operationmode and in the basic operation mode so that the medical staff isprovided with images having always the usual enlargement ratio.

The basic operation mode may be an adult operation mode and thealternative operation mode may be a child operation mode, so that doserate can be optimized for children.

In one particular embodiment, the source and/or the sensor is providedwith collision detection means for detecting a possible collision withthe patient and/or patient positioning means during a motion of thesource and/or the sensor is provided with collision detection means fordetecting a possible collision between the patient and/or patientpositioning means during a motion of the sensor. The collision detectionmeans improve the security of the apparatus. The distance between sourceand sensor can be reduced to a minimum, so that the maximum benefit of areduced distance between source and sensor can be used.

The collision detection means are selected from a group comprisingcapacitive distance sensors, ultrasonic distance sensors, opticaldistance sensors, and time-of-flight optical sensors or any othersuitable sensors.

The distance between source and sensor may also be adjusted depending onthe output of sensor means for determining physical parameters of thepatient. Thus, the distance between source and sensor can be adjusted tothe individual needs of a particular patient.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and properties of the present invention are disclosedin the following description, in which exemplary embodiments of thepresent invention are explained in detail based on the drawings:

FIG. 1 shows a perspective view of an apparatus for combined panoramicand CT-imaging;

FIG. 2 is a side view demonstrating the operation of the apparatus fromFIG. 1 while taking images from an adult patient;

FIG. 3 is a side view demonstrating the operation of the apparatus fromFIG. 1 while taking images from a child;

FIG. 4 is a drawing for illustrating the benefit of a particular imagingmode for children;

FIG. 5 is a side view of a modified apparatus operating in the adultoperation mode;

FIG. 6 is a side view of the modified apparatus from FIG. 5 operating inthe child operation mode;

FIG. 7 illustrates the trajectory of the rotation axis when a CT imageis generated from a child using the apparatus from FIG. 5 ;

FIG. 8 illustrates the trajectory of the rotation axis when a panoramicimage is generated from a child using the apparatus from FIG. 5 ;

FIG. 9 shows a perspective view of a mechanism for moving the sensor;

FIG. 10 is a perspective view of a part of the mechanism from FIG. 9 ;

FIG. 11 is a perspective view of the part from FIG. 10 as seen frombelow;

FIG. 12 is a perspective view of another mechanism for moving thesensor;

FIG. 13 is a perspective view of a further mechanism for moving thesensor as seen from below;

FIG. 14 illustrates collisions that might occur while operating theapparatus;

FIG. 15 shows a modified apparatus provided with collision detectors;

FIG. 16 illustrates the principle of operation of a capacitive collisiondetector;

FIG. 17 illustrates the principle of operation of an ultrasoniccollision detector;

FIG. 18 illustrates the principle of operation of an optical distancesensor; and

FIG. 19 illustrates the principle of a time-of-flight optical sensor.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a perspective view of a combined apparatus 1 for panoramicand CT imaging. Dental panoramic imaging is usually the imaging of avertical image plane that follows the dental arch. Thus an image of thewhole dental arch is formed. Panoramic imaging can also cover thetemporomandibular joint (TMP), the sinus or the mandible or maxilla.Dental CT generally seeks to generate a three-dimensional image of aselected region of interest (ROI) along the dental arch. The ROI usuallycomprises a group of teeth or at least a single tooth. CT can also beused for imaging any region of the head, in particular the ear, nose andthroat.

The apparatus 1 comprises a base 2 on which a pole 3 is attached thatextends in a vertical direction. On the pole 3, an elevation adjustmentmember 4 is mounted that can slide on the pole 3 for adjusting theapparatus 1 to the tallness of a patient to be examined by the apparatus1. A supporting arm 5 is fixed to the elevation adjustment member 4. Thesupporting arm 5 extends in a horizontal direction and holds on its enda rotary arm 6. Motor driven translation and rotation means 7 areinterposed between the supporting arm 5 and the rotary arm 6. Thetranslation and rotations means 7 can be used for rotating and/ortranslating the rotary arm 6 as required for panoramic and CT imaging.The rotary arm 6 can particularly be rotated around a rotation axis 8and the location of the rotation axis 8 can be moved in an x-directionand a y-direction that expands a plane that is perpendicular to therotation axis 8.

At one end of the rotary arm 6, an X-ray source 9 is located. The source9 can be moved along the rotary arm 6 by using adjustment means 10. AnX-ray sensor 11 is further provided at the other end of the rotary arm6. The X-ray sensor 11 is a digital area sensor, usually a flat paneldetector. The sensor 11 can be moved along the rotary arm 6 by usingadjustment means 12.

The adjustment means 10 and 12 are preferably means for performing atranslational movement along the rotary arm 6 but may also bealternative means for varying the location along the rotary arm 6. Forexample, the adjustment means 10 and 12 may also comprise means forperforming a pivoting motion thus varying the relative distance betweenthe source 9 and the sensor 11.

The X-ray source 9 emits X-ray radiation that passes through a head 13of a patient 14, who is usually in a standing position during X-rayexamination. During the acquisition of the X-ray images, the head 13 ofthe patient 14 is held by a head support 15 in a fixed position withrespect to the supporting arm 5. For this purpose, the head support 15can be attached to the elevation adjustment member 4. The head support15 may be a simple bite, on which the patient 14 may bite duringexamination, but can also comprise further means for holding the head 13in a predetermined position during the acquisition of the X-ray images.The head support 15, for instance, may also comprise means that hold thehead 13 of the patient 14 in the area of the temples. The elements ofthe head support 15 may be fixed or movable so that the head support 15can be adapted to the patient 14, in particular to the dimensions of thehead 13.

The operation of the apparatus 1 is controlled by a control unit 16 thatmay be a conventional computer comprising the usual components forexecuting programs such as a processor, means for data transport andstorage as well as various interfaces. The control unit 16 is connectedto components of the apparatus 1 and executes a program for controllingthese components. The control unit 16 controls for instance the motorsassociated with the translation and rotation means 7. The control unit16 can also set the operational parameters of the source 9 such as thecurrent and the voltage of the source 9, since the source 9 is generallyan X-ray tube. As is well-known in the art, the current affects theradiation power of the X-ray radiation emitted by the X-ray tube,whereas the voltage affect the spectrum of the emitted X-ray radiation.The control unit 16 further performs the read-out of acquired image datafrom the digital area sensor 11, processes the image data and presentsthe resulting images on a display 17. The control unit 16 is generallyalso provided with some input means 18 such as a computer mouse or akeyboard that allow an operator to input commands to the control unit16. The display 17 may also be used for entering commands. For example,the display 17 may be a touch screen on which commands can be selectedby the operator from a displayed command menu. The control unit 16 isfinally also arranged for controlling the adjustment means 10 and 12.

The elevation adjustment member 4 is usually operated manually. Beforethe acquisition of the X-ray images, the operator adjust the height ofthe elevation adjustment member 4 such that the patient 14 cancomfortably stand in the apparatus 1.

The apparatus 1 can now be operated in an adult operation mode and in achild operation mode that are further explained referring to FIG. 2 andFIG. 3 .

FIG. 2 illustrates the basic adult operation mode, which is used if thepatient 14 to be examined is an adult person. The X-ray radiationemitted from an anode 19 of the source 9 forms a beam 20. The angularextension of the beam 20 is limited by a primary collimator 21 that islocated between the anode 19 of the source 9 and the patient 14 and isgenerally disposed within a housing 22 of the source 9. In the case ofpanoramic imaging, the beam 20 is a vertically aligned fan shaped beam,whereas for CT a so-called cone beam is used. Beam 20 is transmittedthrough the patient. Beam 20 further passes through an optionalsecondary collimator 23 that is located in front of a sensor plane 24that holds the X-ray sensitive pixels of the sensor. The secondarycollimator 23 can be located within a housing 25 of the sensor 11.

The pixels may be elements converting X-rays into visible light that isdetected and converted into an electrical signal by an associatedphotosensitive element, or elements that convert impinging X-raysdirectly into electrical signals. These electrical signals are convertedinto image data by the associated sensor electronics. The image data areread out by the control unit 16.

For generating a panoramic image of the dental arch, only a selectedregion of the flat area sensor 11 is used, usually only a few columns ofpixels, whereas for CT all pixels of sensor 11 or at least extensiveareas of the sensor 11 are used.

The distance between the anode 19 of the source 9 and the sensor plane24 of the sensor 11 is the so-called source-sensor-distance (=SSD). Thedistance between the anode 19 and an object 26 to be imaged within thehead 13 is the so-called source-object-distance (=SOD). In the case ofpanoramic imaging, the object 26 is a vertical line through a point ofthe dental arch to be imaged by panoramic imaging. In case of dental CTthe object 26 may be a vertical axis of a typically cylindrical ROIcentered on a single tooth or a group of teeth, from which athree-dimensional image shall be generated by using CT. In the case ofCT the object 26 coincides with the rotation axis 8. The ratio of SSD toSOD defines the enlargement ratio.

FIG. 3 illustrates the alternative child operation mode of apparatus 1.In the child operation mode, the relative distance between source 9 andsensor 11 is reduced by using the adjustment means 10 and 12. In FIG. 3, both SSD and SOD are reduced by the same factor thus preserving theenlargement ratio, al-though this is not a mandatory requirement. It isalso possible to move only the source 9 or the sensor 11 or both in anasymmetric manner. Reducing the relative distance between source 9and/or sensor 11 results in a reduced SSD_(r) and a reduced SOD_(r).

The benefit of the alternative child operation mode is illustrated inFIG. 4 . The solid lines show the beam 20 during the adult operationmode, whereas the dashed lines depict beam 20 in the child operationmode. For the sake of simplicity, both SSD and SOD are reduced by thesame factor as in FIG. 3 .

For obtaining a certain signal-to-noise ratio, a certain amount ofradiation energy (Joule=J) must be deposited in each pixel of the sensor11. If the SSD is reduced, the angular extension of the sensor 11appears to be larger as seen from the source 9. Provided that theradiant intensity (Watt/steradian) of the source 9 is kept constant, theamount of energy that is necessary for obtaining a certainsignal-to-noise ratio, is obtained in less time as compared to the adultoperation mode. On the other hand, if the exposure time is keptconstant, the radiant intensity can be reduced. If the SOD is notreduced as shown in FIG. 4 , but kept constant, a reduced radiantintensity results in a diminished absorbed dose rate (J/kgsecond=Gray/second) of the radiation absorbed by the head 13. Since alower absorbed dose rate is less harmful than a higher absorbed doserate, the reduction of the absorbed dose rate is to be preferred. If theSOD is kept constant, the reduction of radiant intensity and thus thereduction of the absorbed dose rate is proportional to (SSD_(r)/SSD)²,wherein SSD_(r) is the reduced SSD. If the SOD is also reduced toSOD_(r), the reduction of the dose rate would be attenuated, becausealso the object 26 appears to be larger as seen from the source 9. Thus,the reduction of the dose rate would then be roughly proportional to(SOD/SOD_(r))² (SSD_(r)/SSD)². If SOD and SSD are reduced by the samefactor and if the radiant intensity is reduced by the square of thisfactor, the absorbed dose rate will remain the same.

It should be noted that a substantial reduction of the absorbed doserate can be obtained by moving the sensor 11 as close as possible to theobject 26. For example, if SSD_(r)/SSD=0.85 corresponding to a 15%decrease, the absorbed dose rate would be diminished by about 30%.

In practice the radiant intensity and thus the absorbed dose rate isdiminished by reducing the current of the source 9. It should be notedthat the dose rate can also be diminished by reducing the voltage of thesource 9 taking into account that the optical thickness of the hardtissue in the body of a child is lower than the optical thickness of thehard tissue in the body of an adult person.

If the SOD is reduced as shown in FIG. 4 , it should be noted that theprimary collimator 21 must be opened more widely for the child operationmode and that the optical path of the beam rays through the patient 14differ in adult and child operation mode as can be recognized from FIG.4. As can further be recognized from FIG. 4 , the dotted lines and thesolid lines of both beams intersect the line of the object 26 at thesame points. The sections of the object 26 are consequently imaged tothe same pixels on the sensor plane 24. The spatial resolution of theobject 26 thus may remain basically the same. It should further be notedthat the enlargement ratio in the child operation mode is the same as inthe child operation mode since both the source 9 and the sensor plane 24are both shifted symmetrically with respect to the rotation axis 8.

The secondary collimator 23 can also be omitted.

In the embodiment depicted in FIG. 1 , the adjustment means 10 and 12are motor driven and operated by the control unit 16. In a simplifiedembodiment, however, the adjustment means 10 and 12 may also be operatedmanually by the operator, for instance by transferring the source 9and/or the sensor 11 to a mark along the rotary arm 6. In this case, theapparatus may be provided with position sensors that allow the controlunit 16 to check the proper positioning of the source 9 and/or sensor11. The control unit 16 can then adapt the operational parameters of thesource 9 to the selected SSD. For example, if the SSD is reduced, theradiant intensity can be reduced accordingly.

FIGS. 5 and 6 show a further modified embodiment. The embodiment shownin FIGS. 5 and 6 comprises an enlarged housing 27, in which the sensor11 can perform a translatory motion in order to adjust the distancebetween the source 9 and the sensor 11. In the modified embodiment, thesource 9 is fixed to the rotary arm 6, and the rotary arm 6 itself ismoved together with the source 9 for diminishing the SOD. At the sametime the sensor 11 is moved within the housing 27 towards the source 9so that the SSD is diminished, too.

The motion of the rotary arm 6 can be performed by the translation androtation means 7, in particular by the means that allow to shift therotation axis 8 in the x- and y-direction. If the source 9 is shiftedtogether with the rotary arm 6, the rotation axis 8 is no longercentered on the object 26 but transferred to some off-center position.This may affect the motion of the rotary arm 6 in the child operationmode.

FIG. 7 illustrates the motion of the rotary arm 6 during CT imaging inthe adult and child operation mode. FIG. 7 particularly depicts variouspositions of the source 9, sensor 11 and a central ray 28 of the beam 20during a CT scan of the object 26 in the child operation mode.

In the embodiments according to FIGS. 2 and 3 , the rotation axis 8 iskept stationary for generating a CT image in the adult operation modeand the child operation mode, and the rotary arm 6 generally performs arotation over 180° around the stationary rotation axis 8 so that thesource 9 and the sensor 11 perform a semicircular motion around therotation axis 8. In the child operation mode of the modified embodimentdepicted in FIGS. 5 and 6 , the rotary arm 6 may be moved such that thesource 9 and the sensor 11 are pivoted around a virtual rotation axis29. The motion around the virtual rotation axis 29 is achieved by movingthe rotation axis 8 along a circular trajectory 30. The circulartrajectory 30 is centered on the virtual rotation axis 29 and therotation angle φ indicating the position of the rotation axis 8 on thecircular trajectory 30 is in phase with the pivoting angle α of therotation performed by the rotary arm 6 around the rotation axis 8. Thisparticular motion along the circular trajectory 30 would preserve theenlargement ratio. It is, however, also possible to change theenlargement ratio in the child operation mode of the modified embodimentdepicted in FIGS. 5 and 6 by moving the sensor plane 24 towards therotation axis 8, by keeping the location of the rotary axis 8 unchangedand by rotating the rotary arm 6 around the rotation axis 8.

FIG. 8 illustrates the motion of the rotary arm 6 during panoramicimaging. As in FIG. 7 , the source 9, the sensor 11 and the central ray28 of beam 20 is depicted in various positions during panoramic imagingon a dental arch 31 of an adult person and a dental arch 32 of a child.During panoramic imaging the rotation axis 8 is moved such that thecentral ray 28 of beam 20 is essential at a right angle to therespective dental arch 31 or 32. The rotation axis 8 is further movedsuch that the enlargement ratio with respect to the vertically alignedplane to be imaged is unchanged. If the embodiment from FIGS. 5 and 6 isused, the rotation axis 8 is moved along a trajectory 33 in the adultoperation mode for imaging the dental arch 31 of an adult person. If achild is to be examined, the distance between source 9 and sensor 11 isdiminished by shifting the rotation axis 8 and by moving the sensor 11along the rotary arm 6 towards the source 9 resulting in a modifiedtrajectory 34. This particular motion along the trajectory 34 wouldpreserve the enlargement ratio. It is, however, also possible to changethe enlargement ratio in the child operation mode of the modifiedembodiment depicted in FIGS. 5 and 6 by moving the sensor plane 24towards the rotation axis 8 and by using the trajectory 33 also for thechild operation mode. In this case the enlargement ratio is preferablyreduced by no more than 10% or 20%.

For the sake of completeness it shall be noted that the embodimentaccording to FIGS. 2 and 3 comprises principally the same trajectory forboth adult and child operation mode provided that the dental arches arethe same or about the same.

The motion of the sensor 11 can be accomplished by various mechanisms.

FIG. 9 is a perspective view of a mechanism 35 for performing aroto-translation with the sensor 11 within the housing 27 of the sensor11. The mechanism 35 is oriented at a right angle with respect to alongitudinal axis 36 of the rotary arm 6. The longitudinal axis 36 ofthe rotary arm 6 is usually parallel to the central ray 28 of the beam20. A base plate 37 of the mechanism 35 is oriented at a right anglewith respect to the longitudinal axis 36 of the rotary arm 6. A guidingrail 38 is affixed to the base plate 37. A guiding block 39 can slide onguiding rail 38, so that a shiftable plate 40 can be shifted along baseplate 37. For controlling the motion of the shiftable plate 40, a motorplate 41 is affixed to one end of the base plate 37. The motor plate 41holds a translation motor 42 that drives a lead screw 43 which extendsalong the rail 38. The lead screw 43 engages a lead screw cartridge 44that is moved along the lead screw 43 if the lead screw 43 is turning.The lead screw cartridge 44 is attached to lead screw block 45, which isaffixed to the shiftable plate 40. If the motor 42 is driving the leadscrew 43, the shiftable plate 40 is thus moved along guiding rail 38.

The shiftable plate 40 holds an extension plate 46, which supportsfurther parts of the mechanism 35. These parts can be recognized fromFIG. 10 . On opposite ends of the extension plate 46, bearings 47 areprovided, each holding a gudgeon 48. On one end of each gudgeons 48, abelt pulley 49 is mounted. Both belt pulleys 49 stretch a cam belt 50that is tensioned by a jockey pulley 51 disposed on one side of the cambelt 50 between both belt pulleys 49. On the opposite portion of the cambelt 50, a fixing plate 52 and drive plate 53 clamp the cam belt 50. Alead screw block 54 is attached to the drive plate 53. The lead screwblock 54 supports a lead screw cartridge 55, that is mounted on a leadscrew 56. For driving the lead screw 56, a motor plate 57 is fixed toone end of the extension plate 46. The motor plate 57 holds a swivelmotor 58, that drives the lead screw 56. If the motor 58 turns the leadscrew 56, the drive plate 53 and fixing plate 52 are moved together withthe cam belt 50. The motion of the cam belt 50 causes a rotation of thegudgeons 48.

As can be recognized from FIG. 11 , the rotation of the gudgeons 48results into a swiveling motion of swivel arms 59 that are mounted tothe other end of the gudgeons 48 below the extension plate 46. Theopposite end of the swivel arms 59 engage in bearings 60 that are heldby a swivel plate 61. The swivel plate 61 finally holds the sensor 11.The swivel plate 61 is provided with channels 62 that allow the heads ofthe gudgeons 48 to pass over the swivel plate 61.

The mechanism 35 can be used for moving the sensor 11 in a lateraldirection with respect to the longitudinal axis 36 of the rotary arm 6in order to adjust the position of the sensor 11 for panoramic or CTimaging. The mechanism 35 can further be used to adjust the distancebetween source 9 and sensor 11 by pivoting the swivel arms 59 so thatthe swivel plate 61 is performing a motion in the direction of thelongitudinal axis 36 of the rotary arm 6. The swivel arms 59 arepreferably pivoted by 180° but may also be pivoted by a smaller angle.In this case, the lateral shift can be compensated by a correspondinglateral movement along the rail 38.

The main advantage of the mechanism 35 is that the sensor 11 can bemoved relatively fast in the direction of the source 9, because forrotating the swivel arms 59 by 180° the lead screw cartridge 55 has tobe moved only over a short distance and the distance covered therotation of the swiveling arms 59 is twice the length of the swivel arms59. A further advantage is that mechanism 35 also allows a lateralmovement of the sensor for adjusting the position of the sensor 11according to the requirements of panoramic and CT imaging.

FIG. 12 depicts an alternative mechanism, where the distance betweensource 9 and sensor 11 is varied by using a scissor mechanism 63. Thescissor mechanism 63 comprises a base 64 that is oriented at a rightangle with respect to the longitudinal axis 36 of the rotary arm 6. Twoparallel rails 65 are attached to the base 64. Sliding blocks 66 aremounted on the rails 65 and hold a folding support 67 comprising struts68, whose one ends are movably attached to the sliding blocks 66. Two ofthe struts 68 are each connected by a central crossing bearing 69 andsupport with their other ends holding blocks 70 that hold a supportplate 71, on which the sensor 11 can be mounted. The folding support 67is driven by a motor 72 that is mounted on the base 64. The motor 72drives a lead screw 73, that is engaged in a screw nut 74 affixed to atraverse 75. The traverse 75 is connected with a pair of sliding blocks66 each mounted on opposite rails 65.

The scissor mechanism 63 also allows a rapid motion of the sensor 11,since the screw nut 74 has to move only a distance along the lead screw73 that corresponds to half the distance the support plate 71 and thusthe sensor 11 is moving towards the source 9.

FIG. 13 shows a linear mechanism 76 that can also be used for varyingthe distance between source 9 and sensor 11. The mechanism 76 comprisesa base 77 provided with rails 78. The base 77 also holds a motor support79 that holds a motor 80 driving a lead screw 81 extending along thelongitudinal axis 36 of the rotary arm 6 and engaging a screw nut 82held by a traverse 83. The traverse 83 extends between the rails 78 andis held by sliding blocks 84 that are mounted on the rails 78. Thesensor 11 is mounted on the traverse 83 such that the longitudinal axis36 of the rotary arm 6 extends along the lead screw 81.

The particular advantage of the linear mechanism 76 is that the linearmechanism 76 is particularly stable and reliable.

It should be noted that the mechanisms described can also be combined.

It should further be noted that the child operation mode can also beused for small adult persons. It is also possible to provide severaldifferent operation modes that are applied depending on the tallness ofthe patient 14 to be examined. Each operation mode then uses a differentdistance between source 9 and sensor 11 for adapting the apparatus 1 tothe particular size of the patient 14. The apparatus 1 may also beprovided with sensor means for determining the size of the patient andfor adjusting the distance depending on the output of the sensor meansin various steps or continuously. These sensor means may be arranged fordetermining one or more physical parameters of the head 13 or patient14. These parameters may be, for instance, the weight of the patient 14,the tallness of the patient 14, dimensions of the head 13, or any othersuitable parameter. These parameters may also be input manually by theoperator of the apparatus 1, if no sensors and not enough sensors areprovided. The control unit 16 can then adapt the operational parametersof the source 9 to the selected SSD. For example, if the SSD is reduced,the radiant intensity can be reduced accordingly by reducing the currentof the source.

If the SSD is reduced as much as possible, collisions may occur. Inparticular, the housing 25 of the sensor 11 may collide with the head 13or head support 15 as illustrated in FIG. 14 , in particular since thehead support 15 can be provided with a protruding temple rest 85. InFIG. 14 , the temple rest 85 is depicted in a closed position, in whichthe temple rest 85 is in contact with the head 13, and in an openposition, in which the temple rest is at a distance of the head 13. Theopen position is indicated by dashed lines whereas the closed positionis shown in solid lines.

As can be recognized from FIG. 15 , the temple rest 85 comprises twocontact portions 86, that contact opposite sides of the head 13 abovethe ears 87. The contact portions 86 are respectively held by branches88, whose lower ends are supported by pivot bearings 89 that are locatedin a base 90. The base 90 may also hold a chin rest 91 and/or bite 92,on which the patient 14 bites during examination in order to fix theposition of the dentition during the scanning process.

As shown in FIG. 14 , it may happen that the housing 25 of the sensor 1collides with the temple rest 85, since the open and closed positions ofthe temple rest 85 are not well-defined. It may further happen that thehousing 25 of the sensor 11 collides with the head 13 of the patient 14due to an unusual shape of the head 13. The patient 14 may, forinstance, have an unusual long back of the head 13 that impedes themotion of the housing 25 along a scanning trajectory.

These collisions can be avoided by direct measurements on the patient'shead 13 or temple rest 85. These measurements may use mechanicalmeasuring tools such as rulers or callipers. Also optical laser scanningtechniques such as LIDAR may be used. A further alternative is the useof cameras in combination with subsequent image recognition to determinethe size of the head 13 and the position of the temple rest 85. In thiscase, passive optical markers can be provided on the temple rest 85 inorder to ensure that the image recognition safely recognizes theposition of the temple rest 85. The position of the temple 85 rest canalso be determined by means of passive radio markers, whose position canbe detected by signals that are emitted and received by aradio-frequency transmitter. The base 90 may finally also be equippedwith a position encoder that detects the angular position of thebranches 88. By using one of these means or any combination of thesemeans, the dimensions of the head 13 can be determined before thepanoramic imaging or scanning for CT starts.

Despite every care in determining the dimensions of the head 13, therisk of a collision during the imaging process remains. The risk of acollision can be diminished or collisions can be avoided at all, if thesensor 11 is provided with a collision detector 93. Such a collisiondetector 93 can be positioned, for instance, in the housing 25 above thesensor plane 24, since the protruding part of the head 13 and the templerest 85 are generally located above the dentition, whose image isgenerated by panoramic or CT imaging.

In order to avoid collisions with the source 9, the source 9 may also beassociated with a collision detector 94.

In the following, various possible embodiments of the collisiondetectors 93 and 94 are described. For the sake of simplicity, theexplanations refer only to the region around the sensor 11 and thehousing 25, but the explanation are also valid for the region around thesource 9 and the housing 22.

FIG. 16 shows an embodiment, in which a capacitive distance sensor 95 isused for detecting collisions. The capacitive distance sensor 95comprises two electrodes 96, that are connected to some sensorelectronics 97, that can be read out by the control unit 16.

The electrodes 96 generate an electrical field 98 that is disturbed ifan object, namely the head 13 or the temple rest 85, approaches theelectrodes 96. Thus, the capacitance of the electrodes 96 changes and animminent collision of the housing 25 with the head 13 or temple rest 85can be detected by the sensor electronics 97 and thus by the controlunit 16.

FIG. 17 shows another embodiment, in which an ultrasonic distance sensor99 is used for detecting collisions. The sensor electronics 97 of theexemplary ultrasonic sensor 99 operates an ultrasonic transceiver 100,which emits and receives an ultrasonic signal 101, that is reflected bythe head 13 or the temple rest 85. The time-of-flight of the ultrasonicsignal 101 is measured and used for determining the distance between theultrasonic transceiver 100 and the head 13 or temple rest 85. The sensorelectronics 97 is consequently also able to detect an imminentcollision.

FIG. 18 shows a further embodiment, in which an optical distance sensor102 is used for detecting collisions. The optical distance sensor 102 isbased on the principle of triangulation. The optical distance sensorcomprises a light source 103, for instance a laser or LED, that emits abeam 104. The beam 104 can be reflected by the head 13 or temple rest85. Reflected light 105 impinges on a position sensitive detector 106.The information on the position, at which the reflected light hits theposition sensitive detector 106, is used by the sensor electronics 97for determining the distance between the optical distance sensor 102 andthe head 13 or the temple rest 85. The sensor electronics 97 of thisembodiment is consequently able to detect an imminent collision.

FIG. 19 shows a fourth embodiment, in which an optical time-of-flight(=TOF) sensor 107 is used for detecting collisions. The optical TOFsensor 107 comprises a light source 108, that emits light pulses 109.The light pulses 109 are reflected at the head 13 or temple rest 85 andreceived by a light detector 110. The time of flight is measured by thesensor electronics 97 and based on the measurement, the distance, thatthe light pulse 109 has travelled between the light source 108 and thelight detector 110, can be determined.

It is an advantage of the optical systems that the results areindependent from the ambient conditions, such as temperature or airhumidity.

The examples for collision detectors shown in FIGS. 16 to 19 shall notbe understood as being limiting. Any other distance sensor can beconsidered, for instance also visual systems that process images fromcamera data for recognizing the risk of a collision with an object inthe field-of-view of the camera.

Finally, it should also be noted that the invention has been describedhere with regard to a dental imaging apparatus. The invention, however,can generally also be used for apparatuses that are used for imaging anyregion in the head 13 of the patient 14, for instance for an apparatusthat is used for imaging the mandible or maxilla, the temporomandibularjoint or the sinus by panoramic imaging and/or that is used for imagingany other region of the head 13 by CT, in particular regions around theear, nose and throat of the patient 14.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, components or groups described inconjunction with a particular aspect, embodiment or example of theinvention are to be understood to be applicable to any other aspect,embodiment or example described herein unless incompatible therewith.

The invention claimed is:
 1. An apparatus for digital imaging in thehead region of a patient comprising: a source for generating X-rayradiation; a sensor for detecting X-ray radiation, which is generated bythe source and passes through the patient, wherein the sensor is asingle sensor for both panoramic imaging and computed tomography in thehead region of the patient; a rotary arm, wherein the source ispositioned in a location at one end of the rotary arm, and the sensor ismovably positioned at another end of the rotary arm opposite the sourceby an adjustment device configured to move the sensor towards thesource, thereby varying the distance between the source and the sensor;a supporting structure for supporting the rotary arm, wherein motordriven translation and rotation means are interposed between the rotaryarm and the supporting structure; and a control unit that controls thesource, the sensor, the adjustment device, and the translation androtation means and that is configured to operate the apparatus in abasic operation mode for a first set of patients and in an alternativeoperation mode for a second set of patients, wherein, in the alternativeoperation mode, the control unit is configured to operate the adjustmentdevice to move only the sensor towards the source, to thereby reduce thedistance between the source and the sensor as compared to the distanceused for the basic operation mode by moving only the sensor towards thesource and the control unit is further configured to reduce a radiantintensity of X-ray radiation generated by the source by reducing an Xray generating current and/or a voltage of the source to thereby reduceX-ray radiation exposure of the patient.
 2. The apparatus according toclaim 1, wherein the control unit additionally shifts a rotation axis ofthe rotary arm.
 3. The apparatus according to claim 2, wherein, forcomputer tomography, the rotation axis is moved on a trajectory around avirtual rotation axis that is located at the object to be imaged.
 4. Theapparatus according to claim 1, wherein the sensor is moved within ahousing that is stationary with respect to the rotary arm.
 5. Theapparatus according to claim 1, wherein the adjustment device isselected from the group consisting of: a mechanism configured for alateral motion with respect to a longitudinal axis of the rotary arm, amechanism configured for a swiveling motion with respect to the rotaryarm, a scissor mechanism for varying the distance between a baseattached to the rotary arm and a support structure of the sensor, alinear mechanism for moving the sensor along a guiding structure in thedirection of the source, and combinations thereof.
 6. The apparatusaccording to claim 1, wherein the adjustment device is motor driven. 7.The apparatus according to claim 1, wherein the apparatus is providedwith a primary collimator that is located between the source and thepatient and that is opened wider in the alternative operation mode thanin the basic operation mode.
 8. The apparatus according to claim 1,wherein an exposure time of the sensor is reduced in the alternativeoperation mode as compared to the basic operation mode.
 9. The apparatusaccording to claim 1, wherein the radiant intensity of the source isreduced by the square of the ratio of the distance between source andsensor in the alternative operation mode to the distance between sourceand sensor in the basic operation mode.
 10. The apparatus according toclaim 1, wherein an enlargement ratio of the panoramic imaging and/orcomputed tomography in the head region of the patient is the same in thealternative operation mode and in the basic operation mode.
 11. Theapparatus according to claim 1, wherein the first set of patients areadult patients and the second set of patients are child patients. 12.The apparatus according to claim 1, wherein the distance between sourceand sensor is adjusted depending on the output of sensor means fordetermining physical parameters of the patient.
 13. The apparatusaccording to claim 1, wherein the source is provided with collisiondetection means for detecting a possible collision of the source withthe patient and/or patient positioning means during a motion of thesource and/or that the sensor is provided with collision detection meansfor detecting a possible collision of the sensor with the patient and/orpatient positioning means during a motion of the sensor.
 14. Theapparatus according to claim 13, wherein the collision detection meansare selected from a group comprising capacitive distance sensors,ultrasonic distance sensors, optical distance sensors, andtime-of-flight optical sensors.
 15. An apparatus for digital imaging inthe head region of a patient comprising: a source for generating X-rayradiation; a sensor for detecting X-ray radiation, which is generated bythe source and passes through the patient, wherein the sensor is asingle sensor for both panoramic imaging and computed tomography in thehead region of the patient; a rotary arm, wherein the source ispositioned at a location at one end of the rotary arm, and the sensor ismovably positioned at another end of the rotary arm opposite the source;a supporting structure for supporting the rotary arm, wherein motordriven translation and rotation means are interposed between the rotaryarm and the supporting structure; the translation and rotation meansbeing configured to shift the rotary arm in the direction of the sensor,whereby the source is positioned nearer to the patient; an adjustmentdevice configured to move the sensor towards the source; a control unitthat controls the source, the sensor, the adjustment device, and thetranslation and rotation means, and that is configured to operate theapparatus in a basic operation mode for a first set of patients and inan alternative operation mode for a second set of patients; wherein, inthe alternative operation mode, the control unit is configured tooperate the translation and rotation means to shift the rotary arm inthe direction of the sensor whereby the source is positioned nearer tothe patient and to operate the adjustment device to move only the sensornearer to the patient, and the control unit is further configured toreduce a radiant intensity of X-ray radiation generated by the source byreducing an X-ray generating current and/or a voltage of the source tothereby reduce X-ray radiation exposure absorbed by the patient.
 16. Theapparatus according to claim 15, wherein the adjustment device isselected from the group consisting of: a mechanism configured for alateral motion with respect to a longitudinal axis of the rotary arm, amechanism configured for a swiveling motion with respect to the rotaryarm, a scissor mechanism for varying the distance between a baseattached to the rotary arm and a support structure of the sensor, alinear mechanism for moving the sensor along a guiding structure in thedirection of the source, and combinations thereof.
 17. The apparatusaccording to claim 15, wherein the first set of patients are adultpatients and the second set of patients are child patients.
 18. Anapparatus for digital imaging in the head region of a patientcomprising: a source for generating X-ray radiation; a sensor fordetecting X-ray radiation, which is generated by the source and passesthrough the patient, wherein the sensor is a single sensor for bothpanoramic imaging and computed tomography in the head region of thepatient; a rotary arm, wherein the source is positioned at a location atone end of the rotary arm, and the sensor is movably positioned atanother end of the rotary arm opposite the source; a supportingstructure for supporting the rotary arm, wherein motor driventranslation and rotation means are interposed between the rotary arm andthe supporting structure; the translation and rotation means beingconfigured to shift a rotation axis of the rotary arm, and to shift therotary arm in the direction of the sensor, whereby the source ispositioned nearer to the patient, and to shift the rotary arm in thedirection of the source, whereby the source is positioned further fromthe patient; an adjustment device configured to move the sensor towardsand away from the source; a control unit that controls the source, thesensor, the adjustment device, and the translation and rotation means,and that is configured to operate the apparatus in a basic operationmode for a first set of patients and in an alternative operation modefor a second set of patients; wherein, in the basic operation mode, thecontrol unit is configured to operate the translation and rotation meansto shift the rotary arm in the direction of the source, whereby thesource is positioned further from the patient, and to operate theadjustment device to move the sensor away from the patient; wherein, inthe alternative operation mode, the control unit is configured tooperate the translation and rotation means to shift the rotary arm inthe direction of the sensor, whereby the source is positioned nearer tothe patient, and to operate the adjustment device to move only thesensor nearer to the patient, and the control unit is further configuredto reduce a radiant intensity of X-ray radiation generated by the sourceby reducing an X-ray generating current and/or a voltage of the sourceto thereby reduce X-ray radiation exposure absorbed by the patient. 19.The apparatus according to claim 18, wherein the adjustment device isselected from the group consisting of: a mechanism configured for alateral motion with respect to a longitudinal axis of the rotary arm, amechanism configured for a swiveling motion with respect to the rotaryarm, a scissor mechanism for varying the distance between a baseattached to the rotary arm and a support structure of the sensor, alinear mechanism for moving the sensor along a guiding structure in thedirection of the source, and combinations thereof.
 20. The apparatusaccording to claim 18, wherein the first set of patients are adultpatients and the second set of patients are child patients.